In recent years, non-contact power transmission systems (non-contact feeding systems) supplying power through a wireless line, namely, in a non-contact manner have been actively developed. Among them, an electromagnetic induction method is drastically commercialized and standardized. The electromagnetic induction method has extremely higher coupling degree between a power transmission side and a power reception side, and allows power feeding with high efficiency. Thus, the electromagnetic induction method is actively commercialized mainly in mobile devices. In addition, standardization of the electromagnetic induction method becomes active, and the standardization is progressed by an industry organization called wireless power consortium (WPC). By standardization, products from different companies are allowed to have compatibility, and thus charging in many combinations of power transmitters and power receivers becomes possible.
A current big issue of the electromagnetic method is an increase in power. Many of power receivers currently commercialized receive power at a level of 1 W, 2.5 W, 5 W, and the like, and an increase in received power to 10 W, 15 W, and the like, is expected.
However, typically, along with the increase in received power of the power receiver, the temperature of the power receiver is disadvantageously raised.
In a power receiver, as a power source integrated circuit (IC) supplying power to a load, for example, a regulator so-called low drop out (LDO) is used. In the LDO, a difference between an input voltage and an output voltage is small, and the output voltage is stabilized. In addition, a power source IC using a DC-DC converter with small power loss and high efficiency is also used. PTL 1 describes a configuration as an example of the power source IC using a DC-DC converter. The invention described in PTL 1 is a non-contact feeding system in which a target voltage is set according to a received power, and the non-contact feeding system performs control based on a magnitude of the received power and control using a target impedance.